1. Field of the Invention
The present invention relates to a semiconductor device and, in particular, to a bleeder resistance circuit using thin film resistors, to a semiconductor device having the bleeder resistance circuit, and to a method of manufacturing the semiconductor device.
2. Description of the Related Art
Large numbers of conventional bleeder resistance circuits using thin film resistors like those shown in FIG. 16 are in use. The term bleeder resistance circuit denotes a circuit for obtaining a predetermined voltage from a power supply voltage. In the bleeder resistance circuit, a plurality of resistance elements arranged in series are connected, and divided voltage is performed to thereby obtain a predetermined voltage. Alternatively, predetermined ratios of the power supply voltage are output.
A MOS transistor 134 is formed on a silicon semiconductor substrate 101. The MOS transistor 134 is formed on the silicon semiconductor substrate 101 with a source region 131 and a drain region 132 separated from each other. A polysilicon gate electrode 133 is formed on the silicon semiconductor substrate 101, through a gate insulating film 100, between the source region 131 and the drain region 132. A field insulation film 135 for element separation is formed on the silicon semiconductor substrate 101 in the periphery of the MOS transistor 134. A polysilicon thin film resistor 139 which becomes a resistance element is formed on the field insulation film 135. The polysilicon thin film resistor 139 becomes a resistor of a portion of a bleeder resistance circuit. An intermediate insulating film 140 is formed on the polysilicon thin film resistor 139, and the source region 131, the drain region 132, and the polysilicon thin film resistor 139 are wired by aluminum wirings 136 formed in contact holes formed in the intermediate insulating film 140.
Several arrangements are known which are not concerned with the electric potential of the wirings on the thin film resistor 139 or the electric potential of the conductors under the thin film resistor 139. Further, polysilicon is often used as the thin film resistor material, and the polysilicon is known, which has the film thickness set to be the same as that of the gate electrode 133 of the MOS transistor 134, with the same polarity, and has temperature characteristics for cases in which the MOS transistor 134 is mounted within the same chip in combination therewith.
However, there is a problem with bleeder resistance circuits using conventional thin film resistors in that the divided voltage ratio is often inaccurate. The resistance value of the thin film resistors changes due to the surrounding electric potentials, in particular due to differences in the surrounding electric potentials. Further, change in the resistance value due to the temperature of the polysilicon thin film resistor (resistance value temperature coefficient) is large for conventional bleeder resistance circuits in which the MOS transistor 134 is mounted within the same chip in combination therewith, and there is a problem in that good divided voltage precision cannot be obtained over a wide range of temperatures.
In order to resolve the aforementioned problems, an object of the present invention is to provide a high precision bleeder resistance circuit having an accurate divided voltage ratio without temperature coefficient of a resistance value. In addition, an object of the present invention is to provide a semiconductor device having high precision and no temperature coefficient which uses the bleeder resistance circuit, for example, a voltage detector, a voltage regulator, and the like.
A first means employed in order to achieve the aforementioned objects relates to a semiconductor device of the present invention, in which a bleeder resistance circuit using thin film resistors has an electric potential of wirings on the thin film resistors and an electric potential of conductors under the thin film resistors nearly equal to the electric potential of each of the resistors. This is because the fact that the resistance value of the thin film resistors changes in accordance with the electric potential of wirings on, and the electric potential of conductors under, bleeder resistance circuits using thin film resistors (particularly polysilicon thin film resistors) has become clear.
A second means employed in order to achieve the aforementioned object relates to the semiconductor device of the present invention, in which a film thickness of polysilicon thin film resistors of a bleeder resistance circuit is made thinner than the film thickness of a gate electrode of a MOS transistor mounted within the same chip in combination therewith. This is because the fact that dispersion in the resistance values becomes smaller as the film thickness of the thin film resistors (particularly polysilicon thin film resistors) becomes thinner and the fact that the temperature dependence of the resistance value becomes smaller even with the same sheet resistance, are clear.
A third means employed in order to achieve the aforementioned objects relates to the semiconductor device of the present invention, in which a p-type impurity is used for the impurity introduced into the polysilicon thin film resistors of the bleeder resistance circuit This is because experiments performed by the inventors of the present invention make it clear that dispersion in the resistance values becomes smaller if the impurity introduced into the thin film resistors is p-type.
A fourth means employed in order to achieve the aforementioned objects relates to the semiconductor device of the present invention, in which the resistance value of the polysilicon thin film resistors of the bleeder resistance circuit is set to 700 xcexa9/square to 1 Kxcexa9/square. This is because it is clear that the temperature dependence of the resistance value of the thin film resistors is from 0 to 100 ppm/xc2x0 C. when the sheet resistance is from 700 xcexa9/square to 1 Kxcexa9/square.
According to the semiconductor device of the present invention, by making the electric potential of wirings on thin film resistors and the electric potential of conductors below the thin film resistors nearly equal to the electric potential of each resistor in a bleeder resistance circuit using the thin film resistors, and by eliminating temperature characteristics, a high precision bleeder resistance circuit having an accurate divided voltage ratio can be achieved. For cases in particular in which polysilicon is used in the thin film resistors, the semiconductor device of the present invention can suppress dispersion in the resistance values, and can eliminate the temperature dependence of the resistance values, by making the film thickness of the polysilicon thin film resistors in the bleeder resistance circuit thin, and in addition, by introducing a p-type impurity into the polysilicon.
Semiconductor devices having high precision and a small temperature coefficient, for example, voltage detectors and voltage regulators, can be obtained by using this type of bleeder resistance circuit.